What is it?

Radioactive substances emit ionising radiation. This energy-rich radiation is a natural phenomenon of substances with unstable atomic nuclei. There are different types of radiation. Being exposed to too much is harmful but it is possible to protect against the associated health risks.

Substances that are radioactive contain radionuclides. These have an unstable atomic nucleus that «decays» spontaneously without any external influence. The radioactivity cannot be influenced either chemically or physically. During decay, energy-rich ionising radiation is emitted. There are three main types:

  • Alpha and beta radiation are produced by the spontaneous alteration of an unstable nucleus into another nucleus.
  • Gamma radiation is produced when an atomic nucleus emits excess energy.

Alpha, beta and gamma radiation have different properties (see box). Of the 118 chemical elements known today, there are more than 2600 atomic species (isotopes). Did you know that only 10% of these have a stable atomic nucleus and 90% have an unstable one?

Avoiding excessively high radiation exposure

Gamma rays and X-rays are electromagnetic waves like light or radio waves, but with a much shorter wavelength; this makes them more energy-rich. Alpha and beta rays are particulate radiation and consist of helium nuclei and electrons. Alpha, beta and gamma rays are all forms of ionising radiation. They transfer so much energy to the atoms and molecules of the irradiated material that electrons are released from the atomic shell and the material becomes ionised (electrically charged). This can cause chemical compounds to break up and result in damage to cells, tissue and organs.

How can we protect ourselves from radiation?

Protection from a radiation source outside the body (external radiation) can be provided by:

  • Shielding the radiation sourc
  • Maintaining a distance from the source
  • Minimising the duration of exposure to the source

Radionuclides can also be taken up by breathing or with foodstuffs and then decay inside the body (internal radiation). The consequences for health of a specific amount of radioactivity are greater when the radiation is internal rather than external. Protection from internal radiation is provided by avoiding ingestion of radionuclides. However, the food we eat and the air we breathe always contain a small amount of natural radioactivity.

Radioactivity decreases with time

The amount of radionuclides and thus radioactivity decreases with time due to radioactive decay. The half-life describes the period of time in which the quantity of a specific radionuclide decreases by half of its initial value. Half-lives range from microseconds to millions of years. For example, caesium-137 formed by nuclear fission has a half-life of 30 years.

Interesting facts about radioactivity can be found in the following publications

Federal Office of Public Health FOPH

Radiation, radioactivity and sound

United States Environmental Protection Agency (EPA)

Radiation: Facts, Risks and Realities

Protection from external radiation

The three types of ionising radiation penetrate to different depths in human tissue. While alpha and beta rays can penetrate only a few millimetres, energy-rich gamma radiation is weakened but scattered in the tissue at the same time.

Image: Nagra

There are different ways of providing protection from radiation. Alpha and beta rays can be completely shielded with relatively little effort, but gamma rays are highly penetrative. However, even gamma rays can be absorbed by suitable materials such as a few centimetres of iron or a few metres of rock or concrete.

Image: Nagra

Protection from external radiation

Ways of protecting from external radiation. Image: Nagra